Cultivar-, stress duration- and leaf age-specific hub genes and co-expression networks responding to waterlogging in barley

Abstract

Mature leaf degradation for supporting the younger leaf growth is a survival strategy for plants under waterlogging stress, but its molecular mechanism is rarely known. In this study, two barley cultivars Laurikka (B1) and Evergreen (B2), differing in waterlogging tolerance, were subjected to 6- or 10- day waterlogging stress during tillering stage. B1 was found more sensitive to waterlogging stress than B2, showing a more rapid leaf chlorophyll loss, but the elongation rate of the youngest leaf had little difference between the two cultivars. The youngest and mature leaves were sampled for dynamic transcriptome analysis. The results showed that 4384 genes were differentially expressed (DEGs) in the two cultivars, displaying significant enrichment of ATP binding, oxidoreductase and hydrolase activity and iron transport. More DEGs were identified between the waterlogging durations and leaf ages, whereas leaf age-specific DEGs were additionally enriched in the photosystem II, thylakoid membrane and carbohydrate binding pathways. A weighted gene co-expression network analysis (WGCNA) of 17669 highly expressed genes was performed to identify hub genes and construct regulatory networks. A cultivar-specific network was dominated by HST1, MLH1 and SYP22 etc., while leaf age-specific networks were largely regulated by chlorophyll metabolism related hub genes CURT1B, PNSL4, and PSY1 etc. This study provided a new insight into deciphering the role of hub genes, networks and pathways with relevance to whole leaves responses to waterlogging stress.